Oxidation number of \(Co\) is \(+3\).
So primary valency is \(3\).
It is an octahedral complex so secondary valency \(6\) or Co-ordination number \(6\).
(આપેલ પરમાણુ ક્રમાંક $: V, 23; Cr, 24, Fe, 26 Ni, 28)$
$V ^{3+}, Cr ^{3+}, Fe ^{2+}, Ni ^{3+}$
$(I)\, Pt(SCN)_2 - 3PEt_3,$ $(II)\,CoBr ·SO_4 · 5NH_3$ $(III)\, FeCl_2 · 6H_2O$
$(i)\, [Cr(NO_3)_3 (NH_3)_3]$ $(ii)\, K_3[Co(C_2O_4)_3]$
$(iii)\, K_3[CoCl_2(C_2O_4)_2]$ $(iv)\, [CoBrCl(en)_2]$